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IV. ONSITE WASTEWATER TREATMENT SYSTEM DESIGN OF OPERATIONAL PARAMETERS AND COMPONENTS SSS§ 3.7. The following is a description and applicable calculations of the wastewater management system structures and operations. SEPTIC TANK CALCULATIONS Septic tanks store the accumulated sludge, scum and effluent (clear zone) volumes, which in turn affect treatment of nitrogen within septic tanks. Detention Time Calculation: Detention Time = 2,000 gal proposed tank capacity x 0.70 (30% volume lost to sludge/scum accumulation) 1.5 (Peaking factor) x 215 gals/day (calculated ADF) Detention Time = 4.3 days. The minimum acceptable detention time is 1.0 days. Therefore, a proposed tank size of 2,000 gallons is adequate for sufficient hydraulic residence time (HRT). FILTER BED DESIGN, EFFLUENT MANAGEMENT AND NITRATE MITIGATION The configuration of the effluent disposal structure will be as a pressurized filter bed: 1,200 gallon Base Tank Capacity (BTC) + Average Daily Flow (ADF) = 1,200 + 215 gpd = 1,415 gals. 1,415 gals x 0.250 (SF) = 354 lineal ft of leachline (LFLL). 354 LFLL x 4 = 1,415 sq ft of filter bed area. The primary disposal area is to consist of the filter bed and adjacent sump: 75 ft N-S x 20 ft E-W = 1,500 sq ft. The septic tank, primary and 100% replacement areas are denoted on the attached OWTS Schematic Plans and the Site Plans produced by Wong Engineers. Effluent management: Influent will enter the septic tank, which will be situated north of the Shop Building. Effluent will be pressurized through an Orenco BioTube with a duplex pump system to be equally distributed through three, 1" dia. perforated laterals with orifices spaced every 5'. At the north end of the filter bed, the contractor is to excavate a 2' wide x 20' long x 8' deep sump. A 1' wide x I' high dam will separate the filter bed from the sump. This will force effluent to remain within the filter bed and be absorbed by the soil at the floor of the filter bed. Although the soil permeability is slow at this 30" depth, the clay type soils are favorable for nitrate mitigation. If these soils cannot manage the effluent flows, or under extreme hydraulic stress from rainfall, effluent will flow over a l' high dam, covered in filter fabric to prevent erosion, and into the sump where permeability is favorable. NLS§ 3.2. In addition to forcing the shallow 30" deep soils to mitigate nitrate loading, a secondary design concept of the wastewater management system for the mitigation of nitrate loading will take advantage of evapotranspiration. An indeterminable percentage of effluent and subsequently the nitrogen within the effluent will be transpired by a deep rooted lawn (e.g., bluegrass) to be planted over the disposal area. 7 Chesney Consulting